Lloyd's mirror: Laser beam interferes with reflection from glass.

Lloyd's mirror: Laser beam interferes with reflection from black-glass mirror. Lloyd's Mirror is a strip of smooth glass about six inches long, painted black on the underside. An expanded monochromatic He-Ne laser beam is sent at a grazing angle to the glass so that part of the beam is reflected from the glass (causing a phase change of _) and interferes with the part of the beam that doesn't hit the glass. The interference fringes are magnified by the -10" diverging lens and projected onto a screen. See Fig.1. The laser beam is the source S1. The light reflected from Lloyd's mirror appears as though it came from virtual source S2. The overlapping region from S1 and S2 (gray area abc) is where interference occurs, showing up as a series of fringes on the screen in the region bc.